Rafting alien biota

Geoff Read g.read at niwa.cri.nz
Sun Apr 28 22:19:58 EST 2002

Annelida members may have seen the publicity surrrounding a short note in 
Nature last week by David Barnes (1a) on a side effect of increased plastic 
debris in the oceans. He says "I ESTIMATE that rubbish of human origin has 
roughly doubled the propagation of fauna in the subtropics and more than 
tripled it at high (>50 deg) latitudes ...". This becomes in the press release 
used in newspapers (1b) that D.B. has "FOUND THAT" floating rubbish has 
almost doubled the spread of alien species. Never mind - he has a valid 
point, though the item is somewhat short on detail of the species being 
transported.  One wonders what NEW species are being transported that 
haven't been transported by the same mechanism of drift debris, on the 
same currents for eons.   

However, to balance this I'd like to mention algal rafting, which he rather 
ignores. Smith's recent observations (2) lead to claims that in the zone 
between Hobart Tasmania and subantarctic Macquarie Island "over 70 
million [algal] rafts [are] afloat at any one time, 20 million of which support a 
holdfast, the habitat supporting the highest faunal diversity in attached kelp 
plants". That's practically a conveyor belt supply (coming towards New 
Zealand by the way). It may not only be important to coastal faunas. Parker & 
Tunnicliffe (3) suggest that seamounts can be colonised this way. The only 
caveat is how long algal rafts can last afloat - Hobday's California Bight paper 
(4) suggests about 100 days. 

Barnes, D. K. A. 2002. Biodiversity: Invasions by marine life on plastic debris
[Brief Communication]. — Nature 416:808 - 809.


Smith, S. D. A. 2002. Kelp rafts in the Southern Ocean. — Global Ecology 
and Biogeography 11(1):67-69.  

Parker, T., & V. Tunnicliffe. 1994. Dispersal Strategies of the Biota on an 
Oceanic Seamount - Implications for Ecology and Biogeography. — 
Biological Bulletin 187(3):336-345.  

Hobday, A. J. 2000. Age of drifting Macrocystis pyrifera (L.) C. Agardh rafts in 
the Southern California Bight. — Journal Of Experimental Marine Biology And 
Ecology 253(1):97-114.  

  Geoff Read <g.read at niwa.cri.nz>

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